Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Utility Patent
1999-02-19
2001-01-02
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S238000, C347S247000
Utility Patent
active
06169566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-impact printer where non-impact printing is performed by, for example, an electrophotographic method and thermal transfer method.
2. Description of Related Art
An electrophotographic printer incorporates, for example, an LED head having a plurality of light emitting diodes (referred to as “LED” hereinafter) aligned in line. The LED head illuminates the charged surface of a photoconductive drum to form an electrostatic latent image thereon. The electrostatic latent image is then developed with toner into a toner image. The toner image is transferred to print paper and subsequently fixed.
The aforementioned conventional apparatus suffers from the following problem.
The LEDs are driven to emit light in accordance with bit data of the print data. In other words, each LED is driven to emit light if a bit is ON, and not to emit light if the bit is OFF. However, it is to be noted that various factors cause variations of characteristics among LEDs and therefore the light intensity of LEDs is not quite consistent. The variations of intensity of light cause differences in dot size of an electrostatic latent image formed on the photoconductive drum. The differences in dot size in turn result in differences in the size of dot or pixel.
If printed images are characters, the differences in dot size are not quite detectable. In contrast, if printed images are photographs, the differences in dot size cause variations of print density, deteriorating print quality. In order to prevent such variations of print density, there has been developed a method of driving LEDs where LED drivers having matched characteristics are selected and used, thereby supplying substantially the same current to individual LEDs.
This method necessitates the selection of matched LED drivers from among a large number of LED drivers. Various operations are involved including determination of an average drive current. The operations require complex alignment and adjustment and increases manufacturing cost. The method is effective in eliminating variations of the intensity of emitted light resulting from variations of drivers, but does not address the problem of variations of the light-emitting characteristic of LEDs.
SUMMARY OF THE INVENTION
An object of the invention is to provide a print head for use in an electrophotographic printer where no detectable difference in print density is recognized.
A non-impact printer include a plurality of print elements. A driver drives the plurality of print elements in accordance with logical states of corresponding bits of print data. First energy specifying data describes an amount of drive energy that should be supplied to each of the plurality of print elements when each of the plurality of print elements are driven. A drive controller subjects the first energy specifying data to random fluctuation to produce second energy specifying data. The drive energy controller supplies an amount of drive energy to each of the plurality of print elements in accordance with the second energy specifying data.
The drive controller includes a non-volatile memory, a random number generator, and an adder. The non-volatile memory stores the first energy specifying data. The random number generator generates random numbers. The adder adds the random numbers to the first energy specifying data to produce the second energy specifying data.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4595948 (1986-06-01), Itoh et al.
patent: 5892532 (1999-04-01), Katakura et al.
Akin Gump Strauss Hauer & Feld L.L.P.
Nguyen Thinh
Oki Data Corporation
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